4 fungicide coverage tips

Over the years, farmers have become proficient at applying herbicides. With the specter of Asian rust, though, fungicides are the new kid on the pesticide block. There are some differences between applying herbicides and fungicides that farmers need to keep in mind, says Scott Bretthauer, University of Illinois Extension application specialist.

Below are four fungicide application tips to remember this summer.

In most cases, applicators apply herbicides before the canopy closes. Not so with fungicides, where you're dealing with a closed canopy. Double this with the fact that fungicides don't thoroughly translocate throughout plants, and it's easy to see why canopy penetration is important. "Fungicides are locally systemic, so they don't go down in the canopy or to new growth," Bretthauer says. "Good deposition is a must."

Droplet size is crucial to canopy penetration. Yet, you walk a fine line when determining droplet size. On one hand, droplets must be small enough to cover sufficient leaf area and to work their way into the canopy. However, droplets must be large enough to minimize drift. Just as is the case with herbicides, drift is a concern.

"You should be worried about drift," says Bretthauer. "It can be toxic to fish and some cultivars of apples." To hit these goals, Bretthauer advises going with a medium-size droplet range between 250 and 350 microns, which 2005 U of I research indicated did a better job for fungicides. That's smaller than the 300- to 600-micron size commonly used for glyphosate applications. However, applying droplets in the 250- to 350-micron range can help ensure adequate canopy penetration while reducing drift. (For comparison's sake, a human hair is 100 microns wide; a pencil lead is 2,000 microns wide.)

"It's best to go with a wide-angle spray nozzle, like a 110-degree nozzle," says Bretthauer. This will enable you to hit the medium droplet size range. One nozzle type to avoid is the hollow cone. "They produce droplets way smaller than 250 microns," says Bretthauer. "They produce drift and can't penetrate the canopy."

"They can dramatically increase coverage in low areas of the canopy," says Bretthauer.

Over the years, farmers have become proficient at applying herbicides. With the specter of Asian rust, though, fungicides are the new kid on the pesticide block. There are some differences between applying herbicides and fungicides that farmers need to keep in mind, says Scott Bretthauer, University of Illinois Extension application specialist.